This invention concerns a class of devices that behave, with respect to sunlight, in such a way as to be helpful for controlling the internal climate or buildings. More precisely, this invention concerns devices that behave as transparent screens during winter time, thus allowing the building, that they define and protect, to receive the full power of the incoming sunlight, and to convert it into useful heat. During summertime, on the contrary, said screens will act as dousers or light blocking devices which totally reject direct sunlight, thus helping towards a considerable reduction of the heat load of the air conditioning plant of said building.
Greenhouses are a special class of buildings that can derive an advantage from using this invention: these structures are designed to capture and retain as much solar energy as possible during wintertime, but they tend to become overheated in summertime, which may damage plants. It is thus customary to cover greenhouses with laths during summertime, or to whitewash their glass covers which will make them less transparent, or to remove them altogether.
On the contrary, by using this invention one can avoid any manual or mechanical operation, since the task of admitting or rejecting solar energy according to the needs of the season is entirely taken up by the optical properties of the covering douser, that will be set up in such a proper way as to fit the various positions of the sun in the different seasons. The physical phenomenon of total reflection of light is well known. It can be observed in all transparent materials, including in particular those known and commonly used in buildings, such as window-glass, an organic glass called plexigas, which is a polymer of methyl-methacrylate, or other materials. In order to practically produce total reflection of light beams, one must use a transparent medium with an index of refraction different from that of the air through which sunlight beams reach the earth surface. Usually available media exhibit refraction indices that are much greater than that of air. It is a usual convention to take as unity the refraction value of the latter, in which case the ratio between the index of refraction of any medium considered and that of air is usually called n. A typical value of n for ordinary window glass is 1.52. However, other glasses with different compositions can exhibit n values as low as 1.45 or even as high as 1.95. Among transparent materials commonly used in buildings, n is 1.49 for plexiglas, 1.53 for vinyl chloride polymer (PVC), 1.586 for polycarbonate, between 1.59 and 1.66 for polystyrene and 1.333 for liquid water. Total reflection cannot be observed in ordinary flat plates with smooth parallel surfaces. It is observed instead, and is well known, in prisms which are used in optics, and is also used, however roughly and with little scientific elaboration, in the so-called "pressed" glass plates, having a frosted, lined, corrugated or otherwise deformed surface, in order to diminish their clarity to the sight. The above described directional properties belong in fact to prisms in general and to surfaces that are shaped like a plurality of prisms. The idea of putting said directional properties to use in connection with the known fact that the sun occupies different, but very precisely defined positions in the sky throughout the year, is however not yet known, and is the basis of the present invention.